As the volume of information handled by a computer is increasing recently, the capacity of a memory device for storing such information is remarkably increasing. A hard disk, optical disk and magnetic tape are the main devices for such a memory device. A hard disk is used as a main memory due to its rapid recording and regenerating capability and random accessibility. An optical disk or magnetic tape is used as an archive or for back-up purposes.
A magnetic tape is superior to an optical disk from the viewpoints of its low price and recording capacity per unit volume. An optical disk is superior to a magnetic tape from the viewpoints of random accessibility and storage. Thus it is desired to increase the recording capacity of an optical disk for obtaining both merits of a magnetic tape and an optical disk.
A technique to increase a recording capacity per unit volume by thinning a thickness of an optical disk has been proposed for the purpose of increasing capacity of an optical disk that is superior from the viewpoints of random accessibility and storage. A technique has been also proposed to suppress plate-vibration of a thin disk and make the thin disk rotate stably by using a stabilizing plate, disclosed in Patent Documents 1 and 2, so as to utilize aerodynamic force generated by air flowing between the thin disk and the stabilizing plate. Patent Document 3 discloses a chucking device using centrifugal force to increase gripping power of a chuck claw.
[Patent Document 1]
    Japanese Patent Kokai Publication No. JP-A-10-308059[Patent Document 2]    Japanese Patent Kokai Publication No. JP-P2006-164488A[Patent Document 3]    Japanese Patent Kokai Publication No. JP-P2004-243430A